1. Field
The exemplary embodiments generally relate to substrate processing systems and, more particularly, to calibration and synchronization of components of the substrate processing systems.
2. Brief Description of Related Developments
Substrate processing equipment is typically capable of performing multiple operations on a substrate. The substrate processing equipment generally includes a transfer chamber and one or more process modules coupled to the transfer chamber. A substrate transport robot within the transfer chamber moves substrates among the process modules where different operations, such as sputtering, etching, coating, soaking, etc. are performed. Production processes used by, for example, semiconductor device manufacturers and materials producers often require precise positioning of substrates in the substrate processing equipment.
The precise position of the substrates is generally provided through teaching locations of the process modules to the substrate transport robot. To teach the locations of the process modules and to precisely place substrates at substrate holding locations, the center of the substrate must be known. Generally automatic substrate or wafer centering algorithms require the utilization of a substrate center fixture in order to define the reference substrate location at zero eccentricity relative to, for example, an end effector of a substrate transport that holds the substrate, where zero eccentricity is where the location of the substrate center coincides with the expected center of the end effector. Generally, the substrate centering fixtures are installed on the end effector manually and are used as a reference surface to position the substrate at a location defines as the zero eccentricity reference. The manual placement of the substrate centering fixture and the manual placement of the substrate relative to the substrate centering fixture may result in operator errors and the generation of particles (e.g. contamination) within the substrate processing equipment. The use of substrate centering fixtures also is performed at atmosphere which means that the environment within the substrate processing equipment is disturbed thereby reducing production time.
Generally the teaching of the substrate transport robot includes detecting a position of the robot and/or substrate carried by the robot with dedicated teaching sensors added to the substrate processing equipment, utilizing instrumented substrates (e.g. including onboard, sensors or cameras) carried by the substrate transport robot, utilizing removable fixtures that are placed within the process modules or other substrate holding station of the substrate processing equipment, utilizing wafer centering sensors that are located within or externally accessible at the process modules, utilizing sensors (e.g. cameras) disposed external to the process modules, or by contacting a target within the process module with the substrate transport robot or an object carried by the substrate transport robot. These approaches to teaching locations within substrate processing equipment may require sensors being placed in a vacuum, may require changes to customer processing equipment and/or tooling, may not be suitable for use in vacuum environments or at high temperatures, may require sensor targets, mirrors or fixtures being placed within the processing equipment, may disrupt a vacuum environment of the substrate processing equipment, and/or may require software changes to the code embedded into the substrate transport robot's and/or processing system's controller.
Other conventional arm temperature compensation algorithms, such as described in United States pre-grant publication number 2013/0180448 and U.S. Pat. No. 6,556,887, may use a reference flag in/on the robot end effector or arm to estimate the amount of thermal expansion by comparing the robot positions when a sensor trips between a reference temperature and a current temperature. This conventional approach inherently assumes that the upper arm and forearm of the robot manipulator are in a steady state condition in such a way that the robot can be modeled as a linear bar at a constant temperature with a certain coefficient of thermal expansion. Generally, the limitation of the conventional arm temperature compensation algorithms is that they do not accurately compensate for position errors for the case where the manipulator links are under temperature transients such as temperature rise or cool down. Such temperature transient scenarios represent more realistic customer use cases since a semiconductor cluster tool can have process modules and load locks at substantially different operating temperatures. These conventional thermal compensation algorithms also generally do not take into account the non-linear effect of the arm kinematics due to their non-linear sensitivity to link angular location with respect to the end effector position.
It is also noted that in conventional implementations, the estimated relative thermal expansion of the robotic manipulator, defined as
      K    S    =            R      ⁢                          ⁢      0              R      ⁢                          ⁢      1      (where R0 is an arm location at a reference temperature and R1 is a new location calculated by control software) is considered to behave linearly and is used to estimate the robotic transport position correction at the placement station position which is located further away from the robot center.
It would be advantageous to automatically center substrates without the use of centering fixtures to effect teaching a substrate transport robot the substrate processing locations within processing equipment without disturbing an environment within the processing equipment or requiring additional instrumentation and/or modification to the substrate processing equipment.